In a conventional geothermal well the production casing terminates in an end portion situated within an expansion spool, which spool is mounted on the upper end of a well head. The end portion of the casing tends to move longitudinally relative to the interior surface of the expansion spool as the production casing expands and contracts due to variations in the temperature to which it is subjected.
In the past, a sliding seal has been effected between an end portion of casing and the expansion spool in which it is disposed by a group of ring shaped packers that encircle the end portion and are positioned between two rigid metallic rings that occupy fixed positions on the casing end portion. The two rings are secured to the end portion of the casing by bolts or the like. Such a sealing structure is shown in the Shambless and Freeman U.S. Pat. No. 3,976,130 that issued Aug. 24, 1976 and is entitled "Packing Means For A Well Head Assembly". A seal such as shown and described in the above identified patent has the operational disadvantage that the pressure exerted by the packers on the interior surface of the expansion spool cannot be varied as the packers wear due to rubbing contact with the interior surface of the expansion spool nor can the pressure that the packers exert on the interior surface of the expansion spool be adjusted when the packers are disposed therein.
A major object of the present invention is to supply a piston assembly that may be removably secured to the end section of a casing string of a geothermal well with the pressure exerted by the packing that forms a part of the piston assembly being adjustable to a desired magnitude on the interior surface of the expansion spool after the packing is situated within the expansion spool. The pressure exerted by the packing may subsequently be adjusted when the expansion spool is lifted a short distance upwardly from the well head on which it is removably mounted.
Yet another object of the invention is to supply a piston assembly in which in a preferred form thereof first and second packings that form a part of the assembly may be adjusted individually to exert desired pressures on the exterior surface of the casing and the interior surface of the expansion spool.
A further object of the invention is to furnish an expansion spool piston that may be made up and secured to casing of a geothermal well after the casing has been cut to extend into an expansion spool a desired distance, but with the use of a wrench, and without altering the structure of the casing end section or the expansion spool.
A still further object of the invention is to furnish a piston assembly that after mounting on an end section of casing may have high temperature resisting grease injected thereinto to provide a circumferentially extending seal.
These and other objects and advantages of the invention will become apparent from the following description of a preferred form thereof and certain alternate forms of the invention.